There are various commercially available systems for the treatment of wastewater pumped from homes and small business. Most systems include an aerobic treatment tank and a clarifier tank, which may be separate from the aerobic treatment tank or within the aerobic treatment tank. Examples of prior art sewage treatment systems are disclosed in U.S. Pat. No. 4,874,002 wherein a clarifier chamber is centrally disposed within the treatment tank, and publication WO 00/15322, wherein a clarifier compartment is similarly disposed within an aeration compartment.
Downstream from the aerobic treatment tank and the clarifier tank, conventional systems employ a disinfectant tank for the final treatment of the wastewater before it is discharged to the environment. The disinfectant system typically includes a holding tank for receiving the wastewater and a discharge pump which may be activated to discharge the treated water from the tank in a variety of ways.
Regardless of the method by which the wastewater is finally discharged, most State and Federal regulations require that the water to be discharged be disinfected to eliminate or at least reduce the bacteria to an acceptable level. For this purpose, it has been common to use chlorinators, particularly chlorinators using tablets or other forms of solid, chlorine generating materials. It is also known to use liquid chlorinators wherein an amount of a liquid chlorine containing composition is injected into the clarified (treated) wastewater.
Typically liquid chlorinators have relied on the use of venturis or venturis-like pumps (venturi systems) to draw the liquid chlorine composition from a storage system into wastewater passing through the venturi system. An inherent problem with these venturi systems is that the wastewater passing there through is generally not totally free of solids. Since typically the nozzles of venturi systems have small diameter openings, there is a likelihood of plugging of the venturi with a concomitant disabling of the liquid chlorine composition infusion system. Examples of typical liquid chlorinators or liquid disinfectant systems employing the aspirating phenomena of venturi systems include U.S. Pat. Nos. 3,996,139; 4,019,983; and 6,627,071. U.S. 2003/0155311 also discloses a system in which liquid chlorine is supplied to a treatment tank due to a venturi effect.
The successful treatment of wastewater with a disinfectant depends on three primary criteria:
(1) the amount of disinfectant added,
(2) the effective mixing of the disinfectant with the wastewater, and
(3) the residence time of the disinfectant in the wastewater.
With respect to the latter item, chlorine as an example obviously needs some period of time to serve its disinfectant roll in the wastewater, but as the residence time of chlorine, and virtually all the disinfectants, in the wastewater increases beyond several hours, the chlorine tends to lose its effectiveness.
There are various difficulties associated with the operation and maintenance of prior art chlorination systems. In addition to the plugging problems discussed above, venturi systems do not always add the desired amount of liquid disinfectant to the tank, and disinfectant is not added at the most desirable times.
Prior art systems for discharging wastewater from the tank which receives and holds the treated wastewater can include a night spray system, an on-demand system, and a dosing system. In the night spray system, discharged wastewater is sprayed into the air during the evening hours generally after 12:00 a.m., and solid tablet disinfectant is commonly added to the system at various times during the day, as a function of incoming water to the pump tank. Solid tablet disinfectants are commonly not favored by homeowners or small businesses, since handling the tablets can be time consuming, and tablets are expensive and have a limited distribution. In a venturi system, a liquid disinfectant is added while pumping wastewater to the environment. One problem is that each night spray system is commonly required by regulating permits to have a periodic, disinfectant residual test, and this test is commonly performed by a certified state licensed maintenance person during daylight hours. As a consequence, a night spray system with a venturi for adding disinfectant may show a low chlorine residual test at 2:00 p.m., although a residual test performed at 1:30 a.m. at night may be satisfactory. As a consequence, there is no assurance that the chlorine residual test accurately-reflects-the residual status of the chlorine in the system during most time periods.
In an on-demand system, wastewater is discharged from the pump or holding tank when the float reaches a selected high value, and discharge continues until the float drops to a selected low value. Disinfectant may be added in a venturi system when the wastewater pump is activated. These systems are inherently ineffective, since the residence time of the disinfectant in the tank may be too short.
The third type of system for discharging wastewater from a pump tank is a dosing system, which may include a drip irrigation system. In this type of system, the discharge pump is cycled briefly in response to a high water level in the tank, and then the pump is deactivated by a timer for a relatively longer period of time, thereby allowing the pumped wastewater to dissipate into the soil through the drip irrigation system. The discharge pump is repeatedly cycled on for a brief period then off for a longer period until the float reaches a low water level, at which point the pump is deactivated. With this type of system, liquid chlorine disinfectant has been added in response to the venturi effect when the discharge pump is cycled on. This procedure creates an inefficiency since at least some of the added chlorine has a very short residence time in the tank before being discharged with the wastewater.
The disadvantages of the prior art are overcome by the present invention, and an improved system for the chemical treatment of wastewater discharged from a pump tank is hereinafter disclosed.